1. Field of the Invention
The present invention is related generally to implantable orthopaedic implants. More specifically, the present invention is related to implantable orthopaedic bone plate inserts.
2. Background Art
Orthopaedic bone plates play a critical role in the healing process of broken bones. Once a bone has been fragmented, it is ideal for the broken bone fragments to be joined back together under compression to promote improved healing. The bone plate is a critical device that is used as a stabilizing bar that bridges the gap in bringing the bone fragments together.
During surgery, a bone plate is inserted next to the fragmented bone of a patient. Compression screws are first placed through the bone plate. They are then anchored into each of the bone fragments and tightened, pulling the bone fragments together under a compression load. Once the compression screws are set in place, locking bone screws are inserted through the bone plate and anchored into the fragmented bone. The locking bone screws in conjunction with the bone plate secure the bone fragments together and ensure that they do not move. However, high tensile stresses are created when the bone fragments are fixated with the locking screws. These tensile stresses could damage the fragile bone fragments and impair the healing process.
The bone plate creates a bridge between bone fragments bearing the tensile load and preventing any movement of the bone fragments. Compression of the bone fragments and complete fixation of the fragments are key elements in promoting improved faster healing of the bone fragments. Bone plates, therefore, are a key element in the bone healing process.
Bone fragmentation, however, is unpredictable. As a result of a traumatic experience, a bone may fragment in multiple erratic locations and present itself in random orientations. Every patient's bones are unique; no two bones will fragment in the same manner in the same orientation. Nevertheless, traditional bone plate technology makes it difficult for a bone plate to be oriented to be utilized correctly for every trauma situation. Bone plates are rigid braces, typically composed of metal, which have historically been designed with fixed threaded holes through which the locking bone screws may not properly align with the matching bone fragment.
It is because of this that additional flexibility is needed to be incorporated into bone plates to afford them increased capability in aligning the locking screw with the matching bone fragments. The present invention is an insert that works in conjunction with an orthopaedic bone plate to increase the number of possible orientations of the locking screw so as to improve the ability of the bone plate to align with bone fragments that are presented in variable orientations with improved bone fragment fixation.
Early bone plate technology comprised bone plates with preexisting threaded holes in combination with threaded locking screws. These earlier bone plate and locking screw combinations secured bone fragments together, however, they lacked the ability to secure bone fragments that were not aligned substantially perpendicular to the threaded locking screw holes of the bone plate.
The preexisting threaded holes of the earlier bone plate technology confined the angle through which the locking screw could be advanced into a bone fragment. For example, with the earlier bone plate and locking screw technology, the physician could only advance the locking screw in the direction of the threaded grooves of the bone plate. The locking screw could only be advanced along the pre-defined perpendicular axis from the bone plate. This limitation created a problem for the physician in that only bone fragments that presented themselves 90° perpendicular from the surface of the bone plate could be secured. Examples of these earlier bone plate and locking screw devices are disclosed in U.S. Pat. No. 5,709,686 to Talus et al.; U.S. Pat. No. 6,206,881 to Frigg et al.; and U.S. Pat. No. 6,306,140 to Siddiqui, the disclosures of which are incorporated herein by reference.
In an effort to increase the degree of freedom in healing fractured bones, plates were developed with locking screws that are able to be inserted at different angles through the bone plate. One such improvement was the development of a bone plate with a tappable contact region as disclosed in U.S. Pat. No. 6,955,677 by Dahners. The disclosure of this patent is incorporated herein by reference. The '677 patent discloses a bone screw with a threaded head that is intended to penetrate into the hole of the bone plate in a tapping fashion. Therefore, the bone screw could be inserted through the bone plate at an angle other than 90° perpendicular from the center of the bone plate cavity. A drawback to this invention, however, is that it utilizes a softer bone plate material which lacks rigidity and stiffness to bear high tensile loads. In addition, over time the softer material of the bone plate could yield to the tensile stresses, resulting in possible movement of the bone fragments that would be detrimental to the proper healing of the bone fragments.
Further, polyaxial screw plate systems have been developed such as those disclosed in U.S. patent application publication 2008/0140130 to Chan et al. as well as U.S. Pat. No. 5,976,141 to Haag et al. The disclosures of these publications are incorporated herein by reference. In the 2008/0140130 application, Chan et al. disclose a threaded head bone screw and drill guide to be used to drill angled holes through the bone plate during surgery. The '141 patent to Haag et al. discloses a bone plate insert that is “snapped” into the bone plate. The insert has an inclined hole that allows the locking or bone screw to be positioned at an angle other than 90° with respect to a plane of the upper or lower surface of the bone plate. These “snap” in inserts are not anchored in place and are prone to slight movements which result in undesirable movement of the bone fragment.
Other previous bone plates rely on a friction fit of the locking screw head to the bone plate to create the connection between insert and bone plate. These frictional fit inserts are predisposed to undesirable movement of the locking screw and, consequently, movement of the bone fragment.
Still other examples of previous bone plate technology are bone plates with a “mushroomed” end providing an enlarged flattened area through which there is an array of pre-defined threaded holes. These types of bone plates are designed to further increase the alignment capability of the locking screw relative to misaligned bone fragments. However, these bone plates, like those previously mentioned, are limited in that they have pre-defined threaded holes or apertures which may not align correctly to the bone fragments after a traumatic experience.
In that respect, the previously described orthopaedic technologies lack the ability to freely rotate about a pivotal axis in securing bone fragments that are off axis from the longitudinal axis plane of the bone plate. In other words, all previously described orthopaedic technologies require that the locking screw pass through the bone plate itself, thereby constraining the locking screw to the limitations of the bone plate.
Accordingly, an orthopedic device is needed that expands the possible locking screw orientations in multiple planes. The present invention is not limited by the geometry of the bone plate in aligning the locking screw to a bone fragment. In addition, the present invention increases the range of angles through which the locking screw can be advanced to a bone fragment. The combination of these inventive features creates multidimensional orientation possibilities of the bone plate.